The present invention relates to safety pressure relief devices and, in particular, to rupture discs, especially reverse buckling rupture discs, and also to methods of manufacturing such discs and of producing failures in such discs which are highly predictable.
Relief devices of the type commonly known as rupture discs have been utilized by industry for many years to provide a safety mechanism to relieve excessive pressure from an overpressurized system or vessel in a reliable manner. The rupture disc is most frequently placed in a vent for a pressure vessel or the like so as to prevent flow of fluid through the vent until the disc ruptures. Through the years, numerous improvements have been made in the rupture disc concept in order to reduce the cost and to improve the reliability of the disc.
A specific type of disc normally referred to as a reverse buckling rupture disc has also been utilized for a number of years and functions under the principle that a dome is formed in the disc which is positioned in the vent such that the dome points toward or faces the pressure side of the vent, that is, the convex side of the dome faces the internal portion or upstream side of the vent wherein pressurized fluid is likely to produce an overpressure which would be dangerous or destructive if not relieved. One advantage of reverse buckling type discs is that systems being protected by the discs can be operated at pressures relatively close to the bursting pressure of the disc without producing fatigue and failure which occurs in many forward bursting discs when operated for long periods of time near the rated bursting pressure of such discs. The dome, when fluid pressure reaches a preselected pressure for which the dome was designed to rupture, starts to collapse, that is, the column or arch of the dome on one side thereof starts to buckle. It is believed that as the arch on one side of the dome starts to collapse, a buckling type wave typically propagates across the surface of the dome to the opposite side of the dome where total collapse eventually occurs. This buckling wave tends to create a whiplash effect on this opposite side of the dome so that the dome at this location is rather violently urged in the direction to which the concave portion of the dome faces (that is, the downstream side of the vent). Many of the reverse buckling rupture discs include knife blades positioned on the concave side of the dome which are normally in spaced relationship to the dome but which are engaged by the dome upon buckling. The knives cut the dome, typically in such a pattern as to cause petals which are held to a flange portion of the disc by tab regions or the like.
Knife blade assemblies for reverse buckling rupture discs add substantially to the cost of such discs and are subject to failure due to corrosive activities of the fluids within the vent system, damage during handling or simply because a mechanic forgets to install the knife assembly which in normal discs results in disc bursting pressures that are many times the rated pressures of such discs. It has, therefore, been a goal of the rupture disc industry to produce a disc of the reverse buckling type which does not include knife assemblies, but which is highly reliable. One reverse buckling rupture disc, which was specifically designed to rupture without the use of knife blades, incorporates the concept of placing grooves, scores or etchings, especially in criss-cross or circular patterns on concave or convex faces of a reverse buckling rupture disc dome. A dome of this type can be seen in U.S. Pat. No. 3,484,817 of Wood. In the Wood device the rupture disc dome buckles, reverses and fractures along the lines of weakness produced by the grooves so as to form petals which are held to the remainder of the rupture disc assembly.
There has been a continuing desire in the rupture disc industry to produce new types of reverse buckling rupture discs which have properties that make them especially suitable for specific purposes, more cost efficient, and/or make the disc more reliable. In particular, new reverse buckling rupture discs are desired which will function without the need for knife blades for cutting the disc on reversal, yet which will remain highly reliable so as to relieve within a relatively close tolerance of the predetermined rupture pressure necessary to protect the vessels or the like which are protected by the disc.
There has also been a problem associated with some reverse buckling rupture discs which do not have knife blade assemblies in that the disc can accidentally be inserted into the vent system with the concave side facing in the wrong direction. Therefore, it is important that the rupture disc relieve in either direction, although the relief in the backwards direction may normally be at a higher pressure.
There is also a problem in some systems with portions of the rupture disc being entrained with the fluid being relieved. Pieces of rupture discs can cause damage to pumps and the like if they are allowed to freely break away from the remainder of the rupture disc assembly upon rupture. Therefore, it is important that the rupture disc dome or petals of the rupture disc dome remain intact after rupture and that they remain attached to a remainder of the disc.